| | '''OpenGL extension NV.blend_equation_advanced |
| | |
| | This module customises the behaviour of the |
| | OpenGL.raw.GL.NV.blend_equation_advanced to provide a more |
| | Python-friendly API |
| | |
| | Overview (from the spec) |
| | |
| | This extension adds a number of "advanced" blending equations that can be |
| | used to perform new color blending operations, many of which are more |
| | complex than the standard blend modes provided by unextended OpenGL. This |
| | extension provides two different extension string entries: |
| | |
| | - NV_blend_equation_advanced: Provides the new blending equations, but |
| | guarantees defined results only if each sample is touched no more than |
| | once in any single rendering pass. The command BlendBarrierNV() is |
| | provided to indicate a boundary between passes. |
| | |
| | - NV_blend_equation_advanced_coherent: Provides the new blending |
| | equations, and guarantees that blending is done coherently and in API |
| | primitive ordering. An enable is provided to allow implementations to |
| | opt out of fully coherent blending and instead behave as though only |
| | NV_blend_equation_advanced were supported. |
| | |
| | Some implementations may support NV_blend_equation_advanced without |
| | supporting NV_blend_equation_advanced_coherent. |
| | |
| | In unextended OpenGL, the set of blending equations is limited, and can be |
| | expressed very simply. The MIN and MAX blend equations simply compute |
| | component-wise minimums or maximums of source and destination color |
| | components. The FUNC_ADD, FUNC_SUBTRACT, and FUNC_REVERSE_SUBTRACT |
| | multiply the source and destination colors by source and destination |
| | factors and either add the two products together or subtract one from the |
| | other. This limited set of operations supports many common blending |
| | operations but precludes the use of more sophisticated transparency and |
| | blending operations commonly available in many dedicated imaging APIs. |
| | |
| | This extension provides a number of new "advanced" blending equations. |
| | Unlike traditional blending operations using the FUNC_ADD equation, these |
| | blending equations do not use source and destination factors specified by |
| | BlendFunc. Instead, each blend equation specifies a complete equation |
| | based on the source and destination colors. These new blend equations are |
| | used for both RGB and alpha components; they may not be used to perform |
| | separate RGB and alpha blending (via functions like |
| | BlendEquationSeparate). |
| | |
| | These blending operations are performed using premultiplied colors, where |
| | RGB colors stored in the framebuffer are considered to be multiplied by |
| | alpha (coverage). The fragment color may be considered premultiplied or |
| | non-premultiplied, according the BLEND_PREMULTIPLIED_SRC_NV blending |
| | parameter (as specified by the new BlendParameteriNV function). If |
| | fragment color is considered non-premultiplied, the (R,G,B) color |
| | components are multiplied by the alpha component prior to blending. For |
| | non-premultiplied color components in the range [0,1], the corresponding |
| | premultiplied color component would have values in the range [0*A,1*A]. |
| | |
| | Many of these advanced blending equations are formulated where the result |
| | of blending source and destination colors with partial coverage have three |
| | separate contributions: from the portions covered by both the source and |
| | the destination, from the portion covered only by the source, and from the |
| | portion covered only by the destination. The blend parameter |
| | BLEND_OVERLAP_NV can be used to specify a correlation between source and |
| | destination pixel coverage. If set to CONJOINT_NV, the source and |
| | destination are considered to have maximal overlap, as would be the case |
| | if drawing two objects on top of each other. If set to DISJOINT_NV, the |
| | source and destination are considered to have minimal overlap, as would be |
| | the case when rendering a complex polygon tessellated into individual |
| | non-intersecting triangles. If set to UNCORRELATED_NV (default), the |
| | source and destination coverage are assumed to have no spatial correlation |
| | within the pixel. |
| | |
| | In addition to the coherency issues on implementations not supporting |
| | NV_blend_equation_advanced_coherent, this extension has several |
| | limitations worth noting. First, the new blend equations are not |
| | supported while rendering to more than one color buffer at once; an |
| | INVALID_OPERATION will be generated if an application attempts to render |
| | any primitives in this unsupported configuration. Additionally, blending |
| | precision may be limited to 16-bit floating-point, which could result in a |
| | loss of precision and dynamic range for framebuffer formats with 32-bit |
| | floating-point components, and in a loss of precision for formats with 12- |
| | and 16-bit signed or unsigned normalized integer components. |
| | |
| | The official definition of this extension is available here: |
| | http://www.opengl.org/registry/specs/NV/blend_equation_advanced.txt |
| | ''' |
| | from OpenGL import platform, constant, arrays |
| | from OpenGL import extensions, wrapper |
| | import ctypes |
| | from OpenGL.raw.GL import _types, _glgets |
| | from OpenGL.raw.GL.NV.blend_equation_advanced import * |
| | from OpenGL.raw.GL.NV.blend_equation_advanced import _EXTENSION_NAME |
| |
|
| | def glInitBlendEquationAdvancedNV(): |
| | '''Return boolean indicating whether this extension is available''' |
| | from OpenGL import extensions |
| | return extensions.hasGLExtension( _EXTENSION_NAME ) |
| |
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| |
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| | |
